The present invention relates to photographic printers. In particular, the present invention relates to a system for automatically identifying subject density failures and providing exposure time corrections.
Photographic printers produce color or black and white prints or transparencies from photographic film originals (generally negatives). High intensity light is passed through the film and imaged on the photosensitive print medium (film or paper). The photographic emulsion layers on the print paper or film are exposed and subsequently processed to produce a print of the scene contained in the original.
A critical portion of a photographic printer is the exposure control, which controls the exposure of the photosensitive medium in order to ensure that the image on the photosensitive medium is properly exposed. The exposure control may utilize inputs from several different sources in order to determine the proper exposure. Most automatic and semi-automatic printers use large area transmission density (LATD) sensors to sample the light transmitted by the negative either prior to or during the exposure. LATD sensors measure the average density of the negative in each of three color channels, typically red, green, and blue. Control of the exposure is then determined using a method known as "integration to grey". With this technique, it is assumed that the colors of the scene in the negative will integrate to grey over the print area, since the scene will typically contain equal amounts of all three colors.
While LATD measurements result in proper exposure for the majority of all prints, there are certain classes of negatives which are misexposed by a printer if exposure is determined solely by integration to grey. One parameter in evaluating the performance of a photographic printer is the "good print yield", which is determined by dividing the number of saleable prints by the number of printable negatives. Remakes (in which the printer misexposes a negative which can be reprinted to give a saleable print) detract from the good print yield. Remakes consist of many broad failure types, which include (1) subject density failures, (2) subject color failures, (3) color failures, (4) density failures, and (5) snow scenes and beach/water scenes.
A subject density failure is a negative in which LATD generated exposure times misexpose the subject (as opposed to the background of the scene). In general, subject density failures require only a plus (+) density correction.
Subject color failures are negatives in which a predominant background color causes the printer to print the subject with an excess of the compliment color. A typical example of a subject color failure is a baby on a red rug; most printers will print the baby with unacceptable cyan color. Subject color failures typically require color correction.
A color failure negative is a negative which has both the subject and background off color in the same color. This is often caused by out of date, overheated film or as a result of incandescent or fluorescent lit scenes. Color failure negatives typically require only color correction from the exposures which could be dictated by the LATD measurements.
Density failure negatives (in which both the subject and background are over- or underexposed) involve only a density correction from the LATD generated print times.
Snow scenes and beach/water scenes may require a small minus (-) density and/or color correction.
Automatic photographic printers have been developed which include systems for recognizing subject density and subject color failure negatives. These systems generally include a density or color measuring system which provides measurements of the transmission density of the negative at defined discrete or continuous areas, as opposed to an average or integrated measurement over the entire negative (i.e. the LATD measurements). The measurements at discrete or continuous areas have been used either to modify the exposure times derived by LATD measurements, or as the sole means of exposure determination. Examples of these mechanisms are described in the following U.S. Pat. Nos. Stimson 3,232,192; Wick et al. 3,245,309; Bowker et al. 3,519,347; Wick et al. 3,523,728; Harvey 3,669,553; Rickard et al. 3,690,765; Huboi et al. 3,694,074; Zahn et al. 3,709,613; Paulous 3,724,947; Huboi et al. 3,790,275; Zahn et al. 3,813,158; Crete et al. 3,873,200; Amano et al. 3,888,580; Dailey 3,944,362; Pone, Jr. et al. 4,017,179.
Photographic printer systems which have been commercially available and which include systems for automatically identifying subject density failure negatives and providing exposure corrections include the Pako Mach II printer, the Kodak 2610 printer, the Agfa 7560 printer with ADK, and the Gretag 3140 printer.